1. Field of the Invention
This invention broadly relates to distillation of hydrocarbyl materials. But more particularly, this invention relates to hydrocarbyl materials comprising a mixture of high and low boiling components, wherein the mixture has a softening point in the range 200.degree. F. to 600.degree. F., as determined in accordance with a modification of ASTM D-3461 (modified ASTM D-3461). The modifications to ASTM D-3461 consist of a stainless steel ball of appropriate dimensions instead of the lead ball, a nitrogen purge exists throughout the heating cell, and testing may be performed to temperatures &gt;180.degree. C.
A softening point throughout this specification and claims is intended to mean that temperature determined and in accordance with modified ASTM D-3461, unless otherwise specifically stated.
Hydrocarbyl material throughout this specification and claims shall mean a material having: a percent by weight of hydrogen in the range 4% to 16%; a percent by weight of carbon in the range of at least 80%, more preferably at least 85% by weight, most preferably at least 90% by weight; a percent by weight of nitrogen in the range 0% to 3%; and percent by weight of sulfur in the range 0% to 4%. The percents by weight are all based upon the total weight of the hydrocarbyl material. Hydrocarbyl material can be pitches derived from petroleum or coal tar.
A WFE process for purposes of this specification and claims includes any process that subjects a thin film to elevated temperatures and reduced pressure to evolve lower molecular weight or more easily volatilized components from higher molecular weight or heavier residues. A WFE process can more narrowly involve: forming a layer on a heated surface while simultaneously providing a pressure in the range 50 to 1,000 microns of mercury (Hg), preferably in the range 100 to 950 microns of Hg. The temperature for the heated surface is generally in the range 600.degree. F. to 850.degree. F., preferably 650.degree. F. to 800.degree. F., and still more preferably 700.degree. F. to 760.degree. F. Generally the layers have thicknesses in the range 0.01 to 0.1 inches, preferably 0.02 to 0.05 inches. The letters "WFE" were selected because a wiped film evaporator can be used to carry out one such WFE process.
2. Description of the Prior Art
Although the invention deals with hydrocarbyl materials in general, this invention is more specifically directed to transforming pitch-like materials from one softening point to another so that they become suitable carbon fiber precursor materials. The carbon fiber precursor materials of this invention are preferably most suitably used in melt blowing of carbon fibers. Examples of melt blowing technology can be found in U.S. Pat. Nos. 4,285,655 to Matsubra; 4,295,809 to Madami; 3,825,380 to Harding; and 4,497,789 to Sawran, et al.
Oxidation of pitch is known to be useful in converting low molecular weight specie, pitch-based materials to higher molecular weight, and higher softening point materials. This is particularly true in the case of roofing fluxes derived from petroleum residuum.
Conoco reports that oxidation of certain mesophase precursors led to a material that could, with heat soaking, be converted into a mesophase material. This is reported in U.S. 4,892,642 of Romine et al., issued Jan. 9, 1990, in a patent entitled Process for the Production of Mesophase, and U.S. 4,892,641 of Fuet al., entitled Process for the Production of Mesophase Pitch, issued Jan. 9, 1990. In each patent, a carbonaceous feedstock substantially free of mesophase pitch is heated at elevated temperature in the presence of an oxidatively reactive sparging gas. Subsequent heat soaking and heat treatment of the oxidized isotropic carbonaceous feed is reported to have resulted in substantial quantities of mesophase.
In a paper entitled Air-Blowing Reactions of Coal Tar Pitch l. Properties of Pitch Modified By Air-Blowing (T. Maeda, et al. Ext. Abst. Nineteenth Biennial Conference on Carbon, University Park, Pa., p.180 (1989)), researchers of Osaka Gas Company Limited report air-blowing of petroleum derived carbonaceous materials to result in isotropic pitches being produced. Air-blowing was reported as a recognized procedure to raise the softening point temperature and coking value of petroleum derived carbonaceous materials. Hence, the procedure is asserted to be applicable and desirable for producing precursor pitch for isotropic general purpose carbon fibers.
U.S. 4,999,099 of Ta Wei Fu and Manfred Katz discloses a process for heating a carbonaceous feedstock at mesophase-forming temperatures while simultaneously passing a sparging gas containing an oxidative component selected from the group consisting of O.sub.2, O.sub.3, H.sub.2 O.sub.2, formic acid vapor, and/or hydrochloric acid vapor with an inert gas component to produce a mesophase pitch that is reported to be especially suitable for the manufacture of carbon fibers. The process involves partial oxidation and partial removal of volatile components as a result of the sparging gas. Not disclosed are any methods for improving the mixing or interaction between the sparging gas and the pitch. In contrast to the instant invention, the disclosed purpose of '099 is to produce mesophase.
U.S. 4,209,500 of Chwastiak, issued Jun. 24, 1980, discloses a process for making high mesophase content pitch in which carbonaceous feed is heated with agitation and a passing of an inert gas through the pitch.
U.S. 3,976,729 and 4,017,327, both issued to Lewis, et al., involve agitating a carbonaceous starting material while heat treating same. In DE No. 2221707 and DE No. 2357477, patent applications of Koppers Company, Inc., the manufacture of isotropic carbon fibers is disclosed. The starting material for carbon fibers is first oxidized with oxygen and then vacuum distilled to remove non-oxidized lower boiling components.
One of the objects of the instant invention is to increase the rate at which a WFE process is carried out. The WFE process is used in this instant invention to increase the softening point of a low softening point hydrocarbyl material. For example, a hydrocarbyl material having a softening point of approximately 250.degree. F. can be increased by means of a WFE process to remove lower molecular weight, more volatile components to produce a higher softening point carbon fiber precursor material. An example of such a process is disclosed in U.S. Pat. Nos. 4,497,789, issued Feb. 5, 1985 (Attorney 5Docket No. 3902OUS), and 4,996,037, issued Feb. 26, 1991.
A pitch such as characterized in the following Table I can be processed in a WFE to produce a carbon fiber precursor material, such as given in Table II, suitable for melt blowing into stabilizable carbon fibers.
TABLE I ______________________________________ TYPICAL ANALYSIS FOR A COMMERCIAL PITCH (A-240) Typical Test Method Value ______________________________________ Softening Point, modified &gt;105.degree. .degree.C. ASTM D-3461 Density, g/cm.sup.3, Beckman 1.23 25.degree. C. Pycnometer Coking Value, wt ASTM D-2416 52 Flash, COC, .degree.C. ASTM D-92 312 Ash, wt % ASTM D-2415 &lt;0.1 Toluene ASTM D-4072 8 Insolubles, wt % Quinoline ASTM D-2318 &lt;0.5 Insolubles, wt % Sulfur, wt % ASTM D-1552 2.5 Carbon, wt % 91 Hydrogen, wt % 6 Distillation, wt % ASTM D-2569 0-270.degree. C. 0 270-300.degree. C. 0 300-360.degree. C. 2.45 Specific Heat Calculated -5.degree. C. 0.271 cal/g 38.degree. C. 0.299 cal/g 93.degree. C. 0.331 cal/g 140.degree. C. 0.365 cal/g Viscosity, cP Brookfield LVT Viscometer, Spindle #18 RPM 325.degree. F. 1.5 2734 350.degree. F. 1.5 866 375.degree. F. 1.5 362 400.degree. F. 3.0 162 ______________________________________
TABLE II ______________________________________ PROPERTIES OF CARBON FIBERS PRECURSOR MATERIAL ASTM Test Property Number Value ______________________________________ Softening Point, modified At least .degree.C. ASTM D- 249 3461 Toluene D-4072 20-40 Insolubles, wt % Coking Value, wt D-2416 65-90 Helium Density, * At about g/cm.sup.3 1.25-1.32 Sulfur, wt % D-1552 0.1-4.0 Carbon, wt % 90-95 Hydrogen, wt % 3-7 Ash, wt % ASTM D- &lt;0.1 2415 Quinoline ASTM &lt;0.5 Insolubles, wt % D-2318 ______________________________________ *Determined by Beckman Pycnometer g/cm.sup.3 at 25.degree. C.
Accordingly, it is one of the objects of this invention to provide a method for producing uniform softening points of hydrocarbyl materials in high yields at commercially useful rates. A commercially useful throughput for a WFE such as sold by Artisan Industries, Inc. of Walthain, Mass., U.S.A., or The Pfaudler Co., Division of Sybron Corporation of Rochester, N.Y., U.S.A., achievable by this invention is an output of at least 3 lb/hr/ft.sup.2, preferably at least 5 lb/hr/ft.sup.2, and most preferably at least 7 lb/hr/ft.sup.2.
It is still another object of this invention to increase the rate at which material such as A-240 pitch can be converted into useful carbon fiber precursor feed for melt blowing or melt spinning. In U.S. Pat. No. 4,497,789, filed Dec. 3, 1982, (Attorney Docket No. 3902OUS) several methods are disclosed for converting A-240 pitch and pitches of that character having a softening point of approximately 250.degree. F. to a material having a softening point in the range of 450.degree. F. to 530.degree. F. A preferred method for producing carbon fiber precursor feeds involves the use of a WFE. Use of a WFE to produce melt blowing carbon fiber precursor material is disclosed in U.S. 4,996,037, issued Feb. 26, 1991.
Were one to take a 250.degree. F. softening point isotropic pitch and introduce it into a WFE, the rate of output from the WFE is roughly 3-5 lb/hr/ft.sup.2. Accordingly, it would be desirable to find a way to increase the rate at which a pitch can be processed to higher softening points in conjunction with a WFE.
These and other objects that will become clear based upon this disclosure have been found achievable by the processes of this invention.